The correct answer is that the 'ip igmp version 3' command enables IGMPv3 on the interface, which provides the source filtering capability required for Source-Specific Multicast (SSM) when used with PIM sparse-mode. Unlike IGMPv2, which only allows hosts to join a multicast group address, IGMPv3 permits hosts to specify both the group and the exact source address in their membership reports, enabling the router to forward traffic only from that source. On the ENCOR 350-401 exam, this question tests your understanding of how SSM relies on IGMPv3 to differentiate between any-source and source-specific group joins, often appearing alongside PIM sparse-mode configurations. A common trap is assuming IGMPv2 is sufficient for SSM, but without IGMPv3, the router cannot enforce source filtering, breaking SSM operation. Memory tip: think of IGMPv3 as the "source selector"—v2 says "I want the channel," v3 says "I want the channel from this specific host."
CCNP Network Function Virtualization Practice Question
This 350-401 practice question tests your understanding of network function virtualization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Given the following configuration:
interface GigabitEthernet0/0
ip address 10.1.1.1 255.255.255.0
ip pim sparse-mode
ip igmp version 3
What is the purpose of the 'ip igmp version 3' command?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It enables IGMP version 3, which allows hosts to join multicast groups from specific sources, supporting SSM.
The 'ip igmp version 3' command enables IGMPv3 on the interface, which supports Source-Specific Multicast (SSM) by allowing hosts to specify both the multicast group and the source address in their membership reports. This is essential for SSM operation with PIM sparse-mode, as IGMPv3 provides the source filtering capability that IGMPv2 lacks.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
It enables IGMP version 3, which allows hosts to join multicast groups from specific sources, supporting SSM.
Read the scenario before looking for a memorised answer.
✗
It enables IGMP version 3, which increases the number of multicast groups supported to 1024.
Why it's wrong here
Incorrect. IGMP version does not limit the number of groups; that is platform-dependent.
✗
It enables IGMP version 3, which is required for PIM dense-mode operation.
Why it's wrong here
Incorrect. PIM dense-mode does not require IGMPv3; IGMPv2 is sufficient.
✗
It enables IGMP version 3, which disables IGMP snooping on the interface.
Why it's wrong here
Incorrect. IGMP snooping is a separate feature; IGMP version does not control snooping.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that IGMPv3 is simply a 'newer version' with generic improvements, when in fact its key differentiator is source-specific filtering for SSM support.
Detailed technical explanation
How to think about this question
IGMPv3 (RFC 3376) introduces source-specific group membership reports, enabling hosts to use the 'INCLUDE' or 'EXCLUDE' filter modes to join groups from specific sources. In a real-world SSM deployment, this allows a receiver to join (S,G) channels directly, reducing multicast flooding and simplifying routing by eliminating the need for RP (Rendezvous Point) discovery. Without IGMPv3, SSM cannot function because IGMPv2 only supports (*,G) joins.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Function Virtualization — This question tests Network Function Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: It enables IGMP version 3, which allows hosts to join multicast groups from specific sources, supporting SSM. — The 'ip igmp version 3' command enables IGMPv3 on the interface, which supports Source-Specific Multicast (SSM) by allowing hosts to specify both the multicast group and the source address in their membership reports. This is essential for SSM operation with PIM sparse-mode, as IGMPv3 provides the source filtering capability that IGMPv2 lacks.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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